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Dey KK Bhattacharyya R Kumar A 《Journal of magnetic resonance (San Diego, Calif. : 1997)》2004,171(2):259-363
NMR photography has gained significant attention as a method of storing and retrieving information using NMR spectroscopy. Among the commonly practiced methods the most important is the frequency encoding by use of a multi-frequency pulse on a liquid crystal molecule. We propose and demonstrate another robust method which relies on spatial encoding. Spatial information is mapped onto the spectrum, if excited and recorded in the presence of a gradient. The encoding is performed by applying a multi-frequency pulse in the presence of a gradient. The subsequent acquisition, under a gradient, helps storing this spatial information on a one-dimensional spectrum. Series of such spectra can also store two-dimensional patterns. This procedure is described and exemplified in this paper. 相似文献
264.
Microporous hexagonal niobium phosphate synthesized using neutral surfactants of molecular length, C6 to C10 hydrocarbons, by a supramolecular templating mechanism (S0I0) possesses strong hydrophilic character, which leads to high selectivity for catechol formation (95.3%) in the presence of protic solvent (MeOH) in the hydroxylation of phenol using aqueous H2O2. 相似文献
265.
A facile synthesis of naturally occurring (±)-machicendiol and its analogs has been accomplished in moderate to good yield from 2-aryl-5-formly-7-methoxy-benzofurans through two simple, efficient approaches involving the application of Reformatsky reaction and Claisen condensation. 相似文献
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In single crystals of 2H-NbSe2, we identify for the first time a crossover from a weak collective to a strong pinning regime in the vortex state which is not associated with the peak effect phenomenon. Instead, we find the crossover is associated with an anomalous history dependent magnetization response. In the dc magnetic field (Bdc)-temperature (T) vortex matter phase diagram we demarcate this pinning crossover boundary. We also delineate another boundary which separates the strong pinning region from a thermal fluctuation dominated regime, and find that a peak effect appears on this boundary. 相似文献
268.
Rele S Song Y Apkarian RP Qu Z Conticello VP Chaikof EL 《Journal of the American Chemical Society》2007,129(47):14780-14787
Self-assembling peptides have been previously designed that assemble into macroscopic membranes, nanotapes, and filaments through electrostatic interactions. However, the formation of highly ordered collagen-like fibrils, which display D-periodic features, has yet to be achieved. In this report, we describe for the first time a synthetic peptide system that self-assembles into a fibrous structure with well-defined periodicity that can be visualized by transmission electron microscopy (TEM). Specifically, we designed and synthesized a peptide that utilizes charged amino acids within the ubiquitous Xaa-Yaa-Gly triad sequence to bias the self-assembly into collagen-like homotrimeric helices that are capable of fibrillogenesis with the production of D-periodic microfibers. Potential molecular mechanisms for peptide assembly into triple-helical protomers and their subsequent organization into structurally defined, linear assemblies were explored through molecular dynamics (MD) simulations. The formation of thermodynamically stable complexes was attributed to the presence of strong electrostatic and hydrogen bond interactions at staggered positions along the linear assembly. This unexpected mimicry of native collagen structure using a relatively simple oligopeptide sequence establishes new opportunities for engineering linear assemblies with highly ordered nano- and microscale periodic features. In turn, the capacity to precisely design periodic elements into an assembly that faithfully reproduces these features over large length scales may facilitate the fabrication of ordered two- and three-dimensional fiber networks containing oriented biologically, chemically, or optically active elements. 相似文献
269.
The current level of laboratory instrumentation and computational resources allows X-ray powder diffraction to be implemented into the toolbox of organic chemists, providing a means for rapid (i.e., within a day) structural characterization of organic solids, without the need for single crystals. We illustrate such use of powder diffraction using two case studies of molecular cocrystals of trifluoroacetic acid and malonic acid, involving theobromine, a model active pharmaceutical ingredient. We also report on a previously unobserved conformation of malonic acid in the solid state. 相似文献
270.
Diffraction gratings: aberrations and applications 总被引:1,自引:0,他引:1
Diffraction grating is an optical instrument, which is advantageously used for scientific research in spectroscopy and spatial filtering. It has many other applications in science and technology such as wavelength selectors for tuneable lasers, selective surfaces for solar energy, masks for photolithography, beam sampling mirrors for high power lasers, spectrometers in extreme UV and X-ray regions for space optics, metrology, phase measuring interferometry and pattern recognition, etc. Although the holographic gratings have many advantages over the ruled gratings but they have not yet eliminated completely the classical ruled gratings as the ruled gratings have their own importance in many applications. Therefore, in this article, both the ruled and holographic gratings will be discussed, in particular, their focusing properties, aberrations, and their applications. 相似文献